3.5 Cryo-PTSA Scale-up Using Zeolites
3.5.1 CH 4 /CO 2 Separation by Cryo-PTSA Using Binderless Zeolite 13X
Pilot scale can be used to investigate new processes or improve the existing ones and
to provide valuable data for large-scale production. At the pilot scale, it is possible to
perform the first studies on the influence of several factors such as temperature,
pressure, pH, and composition, among others. It is important also to gather detailed
process data and to optimize the process to the fullest. As an example of the design
and optimization of an industrial adsorptive-based process, we will describe the
scaling up strategy, followed by Moreira et al. [29].
They started with choosing the adsorption column size and considered a diameter
of 3.5 m based on the transport limitations. The length of the column was determined
to take into consideration the limitations in the mass transfer and temperature,
effective use of the adsorbent of 65%, and a bed porosity of 0.4. The authors
obtained a column length of 6 m, after assuming an adsorption time of 8,500 s, a
CO 2 feed molar flow rate of 74.52 kmol/h, working capacity of 8.41 mol/kg, and an
apparent adsorbent density of 1,200 kg m
À3 . The mathematical model used to
simulate the cycles is the same described above for PSA, where the equation of
state used was the GERG-2008, instead of ideal gas law, to cover the range of
temperature and pressure used in the study and to obtain the most realistic results.
To obtain a purified CH 4 stream with low CO 2 content, a cycle with four steps
was conceived. The cycle started with pressurization in co-current feeding the target
mixture containing 99.1% CH 4 and 0.9% CO 2 , followed by the blowdown in
countercurrent and at last a purge step with a heated stream. During the pressurization and adsorption steps, an enriched CH 4 stream with a CO 2 content lower than
50 ppm was produced. In the blowdown step, where the system pressure decreased
from 4,000 to 500 kPa countercurrently, part of the CO 2 desorbed and exit the
column. During the purge step, part of the product stream was fed countercurrently
to the bed at 500 kPa and 473 K, allowing the additional desorption of CO 2 cleaning
the bed. The pressurization step had a duration time of 8,450 s, followed by the
blowdown step with 300 s and purge/heating step of 8,150 s.
To perform the Cryo-PTSA simulations, it was assumed that the column was
initially filled with a gas mixture containing 50 ppm of CO 2 in CH 4 at 473 K and
500 kPa. Transport parameter values, as well as stream conditions necessary for
modeling, are presented in Table 14.
As can be possibly observed in the molar fraction history during the adsorption
step, all CO 2 fed to the column was adsorbed, resulting in a product stream with a
CO 2 amount below 50 ppm. During the blowdown and heating step, the column was
regenerated, and it is possible to obtain a maximum CO 2 amount of 14% during the
heating step. The average CO 2 amount produced in a CO 2 -enriched stream is around
8.8%. The simulation showed high recovery of CH 4 , approximately 90.7%, is
possible to obtain a product stream with 41.8 ppm of CO 2 in methane. Additionally,
methane productivity of 100.1 mol kg ads
À1 h
À1 was obtained.
184
V. F. D. Martins et al.
3.5.1 CH 4 /CO 2 Separation by Cryo-PTSA Using Binderless Zeolite 13X
Pilot scale can be used to investigate new processes or improve the existing ones and
to provide valuable data for large-scale production. At the pilot scale, it is possible to
perform the first studies on the influence of several factors such as temperature,
pressure, pH, and composition, among others. It is important also to gather detailed
process data and to optimize the process to the fullest. As an example of the design
and optimization of an industrial adsorptive-based process, we will describe the
scaling up strategy, followed by Moreira et al. [29].
They started with choosing the adsorption column size and considered a diameter
of 3.5 m based on the transport limitations. The length of the column was determined
to take into consideration the limitations in the mass transfer and temperature,
effective use of the adsorbent of 65%, and a bed porosity of 0.4. The authors
obtained a column length of 6 m, after assuming an adsorption time of 8,500 s, a
CO 2 feed molar flow rate of 74.52 kmol/h, working capacity of 8.41 mol/kg, and an
apparent adsorbent density of 1,200 kg m
À3 . The mathematical model used to
simulate the cycles is the same described above for PSA, where the equation of
state used was the GERG-2008, instead of ideal gas law, to cover the range of
temperature and pressure used in the study and to obtain the most realistic results.
To obtain a purified CH 4 stream with low CO 2 content, a cycle with four steps
was conceived. The cycle started with pressurization in co-current feeding the target
mixture containing 99.1% CH 4 and 0.9% CO 2 , followed by the blowdown in
countercurrent and at last a purge step with a heated stream. During the pressurization and adsorption steps, an enriched CH 4 stream with a CO 2 content lower than
50 ppm was produced. In the blowdown step, where the system pressure decreased
from 4,000 to 500 kPa countercurrently, part of the CO 2 desorbed and exit the
column. During the purge step, part of the product stream was fed countercurrently
to the bed at 500 kPa and 473 K, allowing the additional desorption of CO 2 cleaning
the bed. The pressurization step had a duration time of 8,450 s, followed by the
blowdown step with 300 s and purge/heating step of 8,150 s.
To perform the Cryo-PTSA simulations, it was assumed that the column was
initially filled with a gas mixture containing 50 ppm of CO 2 in CH 4 at 473 K and
500 kPa. Transport parameter values, as well as stream conditions necessary for
modeling, are presented in Table 14.
As can be possibly observed in the molar fraction history during the adsorption
step, all CO 2 fed to the column was adsorbed, resulting in a product stream with a
CO 2 amount below 50 ppm. During the blowdown and heating step, the column was
regenerated, and it is possible to obtain a maximum CO 2 amount of 14% during the
heating step. The average CO 2 amount produced in a CO 2 -enriched stream is around
8.8%. The simulation showed high recovery of CH 4 , approximately 90.7%, is
possible to obtain a product stream with 41.8 ppm of CO 2 in methane. Additionally,
methane productivity of 100.1 mol kg ads
À1 h
À1 was obtained.
184
V. F. D. Martins et al.